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Of the filtrate, 250 c.c. are evaporated to dryness, gently ignited to expel
the ammonium salts, the residue being dissolved in hot water and the solu-
tion filtered through a small filter, which is well washed with hot water.
The liquid is evaporated to a small volume (about 10 c.c.) in a porcelain or
glass dish on a steam-bath and the potassium determined by one of the
following methods :
(a) PLATINUM CHLORIDE METHOD. The small quantity of liquid is
evaporated to a syrup with 25 c.c. of 10% platinum chloride solution, being
frequently stirred with a glass rod ; 50 c.c. of alcohol (85-5% by
volume = 80% by weight) are then stirred in and after an hour the liquid
filtered through a filter dried at 100° and tared, the precipitate being well
washed with alcohol of the above strength, dried at 100° and weighed.1
K2PtCl6 x 0-194 = K20.
(&) PERCHLORATE METHOD. The concentrated solution, in a glass
dish, is evaporated on a water-bath with about 15 c.c. of perchloric acid of
D 1-12 (about 20%) until the hydrochloric acid is completely expelled and
white fumes of perchloric acid appear. On cooling, the residue is mixed
with 25 c.c. of approximately 95% alcohol containing 0-2% of perchloric
acid, all lumps being broken up with a glass rod. After the lapse of 30
minutes, the precipitate is collected on a Gooch crucible previously dried
at 120° and weighed, washed with not more than 70-75 c.c. of 95% alcohol
containing 0-2% of perchloric acid and finally with pure 95% alcohol. It
is then dried at 120° and weighed. The content of potash is expressed as
percentage of K20.
A crystalline powder, greyish or sometimes reddish, yellowish or bluish
according to the impurities it contains ; the pure salt is colourless.
The determinations and tests to be made are as follows :
1. Moisture.—5 grams are heated at 110-120° to constant weight.
2. Nitrogen.—10 grams are dissolved in water to I litre and 50 c.c.
of this solution (= 0-5 gram of substance) distilled with sodium hydroxide
(see General Methods, 3, A).
3. Fixed Residue.—3 grams are'ignited until no further evolution of
volatile matters takes place.
4. Thiocyanates.—2 grams are dissolved in 20 c.c. of water and a little
hydrochloric acid and ferric chloride added: in presence of thiocyanates
a red coloration forms.
1 Instead of a filter-paper a Gooch crucible may be used. The precipitate is col-
lected in this, dried at 100° and weighed. The crucible is then washed with boiling
water to dissolve the precipitate, again dried and weighed. The loss in weight gives the
potassium platinichloride.ilisers, HI -jo ^nuiis (according to the supposed tiehuesK